This invention relates to a fireplace, and, in particular, to a cooling passageway disposed within an air-cooled housing enclosing the combustion chamber of the fireplace.
Known in the art are a multitude of different types of combustion apparatus, including fireplaces such as freestanding models and zero clearance models. These models of fireplaces, and most particularly zero clearance fireplaces, commonly include housings or shells formed of conductive material such as sheet metal that surround the combustion chambers or fireboxes whereat combustion of fuel occurs and include a transparent glass door assembly. The walls of the housing are typically constructed in spaced relationship with some or all of the walls of the combustion chamber, including the bottom wall and top wall which form the floor and ceiling of the combustion chamber. The resulting space or plenums provided between the combustion chamber and housing permits the formation of passageways suitable to circulate air. Existing fireplaces have used these passageways to circulate air to serve a number of nonexclusive purposes, including the cooling of the exterior of the housing. Keeping the outer housing cool is of significant importance in zero clearance fireplaces where the materials externally adjacent the housing may be combustible.
One problem with some existing fireplaces is that under certain operating condition not enough air to cool the housing to a desirable level flows through the cooling passageways. In a known fireplace construction which uses an induced draft within a cooling passageway, rather than a forced draft created by a fan, air from an upper plenum of the cooling passageway which is disposed above the fireplace combustion chamber discharges directly into the forward region of the combustion chamber. This outlet air then passes rearwardly through the combustion chamber to mix with the combustion products and then pass into the flue. While in such a construction cooling air is drawn through the cooling passageway when the combustion chamber access doors are closed, conditions within the combustion chamber are such that induced air flow through the upper plenum is severely curtailed or halted when the access doors are open. Consequently, when the fireplace doors are open during operation, the stagnated air within the cooling passageway increases in temperature over time due to the heat radiating from the combustion chamber, and an undesirable increase in the temperature of the outer housing ultimately results.
Another problem with some existing fireplaces pertains to their inability to maintain at relatively low temperatures the upper forward portion of the outer housing. This problem often persists despite the fact that a cooling air plenum above the combustion chamber is provided. In particular, the air within the cooling passageway upper plenum is frequently discharged or routed downwardly in the direction of the combustion chamber. Because hotter air rises, the air within the upper plenum more inclined to be drawn through the upper plenum is the air closer to the outlet, that is, the cooler air flowing near to the combustion chamber. The hotter air which migrates upwardly tends to stagnate in the upper forward portion of the outer housing, raising the temperature thereof, when the induced draft through the plenum is not strong enough to pull the entire volume of air through the upper plenum.
What is needed in the art is a fireplace having an air-cooled outer housing which promotes adequate cooling of the forward portion of the top wall of the outer housing.
An additional need is a fireplace having an air-cooled outer housing which is adequately cooled by an induced draft of cooling air when the access doors to the combustion chamber are either open or closed.